Diamond is an ideal material for many applications due to its extreme hardness, atomic density, and high thermal conductivity. As such, large diamond bodies would benefit numerous applications, including those involving tools, substrates, electronic components, etc. Diamond bodies comprised of essentially a single crystal orientation are highly sought after, particularly in association with semiconductors and heat spreaders.
For example, as computers and other electronic devices become smaller and faster, the demands placed on semiconductor devices utilized therein increase geometrically. These increased demands can create numerous problems due to the accumulation of charge carriers, i.e. electrons and holes that are intrinsic to quantum fluctuation. Accumulation of the carriers creates noise, and tends to obscure electrical signals within the semiconductor device. This problem is compounded as the temperature of the device increases. Much of the carrier accumulation may be due to the intrinsically low bonding energy and the directional anisotropy of typical semiconductor crystal lattices. Another problem may be a further result of current semiconductor materials. These semiconductors tend to have a high leaking current and a low break down voltage. As the size of semiconductor transistors and other circuit elements decrease, coupled with the growing need to increase power and frequency, current leak and break down voltage also become critical.
As power and frequency requirements increase and the size of semiconductor components decreases, the search for materials to alleviate these problems becomes crucial to the progress of the semiconductor industry. One material that may be suitable for the next generation of semiconductor devices is diamond. The physical properties of diamond, such as its high thermal conductivity, low intrinsic carrier concentration, and high band gap make it a desirable material for use in many high-powered electronic devices.
Methods for creating diamond layers can include known processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and growth in high pressure apparatuses. Various CVD techniques have been used in connection with depositing diamond or diamond-like materials onto a substrate. Typical CVD techniques use gas reactants to deposit the diamond or diamond-like material in a layer, or film. These gases generally include a small amount (i.e. less than about 5%) of a carbonaceous material, such as methane, diluted in hydrogen. A variety of specific CVD processes, including equipment and conditions, are well known to those skilled in the art.
Though single crystal diamond films can be grown using CVD processes, they are currently very expensive and slow to grow to a sufficient thickness to be useful as a diamond body or a diamond substrate. CVD deposited polycrystalline diamond (PCD) layers, on the other hand, can be grown to a sufficient thickness more rapidly and with less expense. Grain boundaries inherent to the PCD layer, however, will create dislocations in the crystal lattice of any material deposited thereon, thus precluding their use in those applications requiring high quality crystal lattices. PVD processes create similar grain boundary issues, and are thus not desirable for many applications.
Unfortunately, currently known high pressure crystal synthesis methods also have several drawbacks which limit their ability to produce large, high-quality crystal bodies. For example, isothermal processes are generally limited to production of smaller crystals useful as superabrasives in cutting, abrading, and polishing applications. Temperature gradient processes can be used to produce larger diamonds; however, production capacity and quality are limited. Several methods have been utilized in an attempt to overcome these limitations. Some methods incorporate multiple diamond seeds; however, a temperature gradient among the seeds prevents achieving optimal growth conditions at more than one seed. Some methods involve providing two or more temperature gradient reaction assemblies such as those described in U.S. Pat. No. 4,632,817. Unfortunately, high quality diamond is typically produced only in the lower portions of these reaction assemblies. Some of these methods involve adjusting the temperature gradient to compensate for some of these limitations. However, such methods cost additional expense and require control of variables in order to control growth rates and diamond quality simultaneously over different temperatures and growth materials.
Therefore, apparatuses and methods which overcome the above difficulties would be a significant advancement in the area of high pressure crystal growth, and continue to be sought.